The present invention relates to an arc welding electrode having a fine powder or metallic coating which volatilizes at arc temperatures and forms a partial pressure in the resultant gas envelope that serves to neutralize volatile impurities; to improve the arc; and to distribute heat through condensation and radiant heat transfer in all forms of arc welding.
Arc welding encompasses a variety of methods for joining metals, all of which involve the use of an electric arc as a source of heat to melt and join metal. The arc is initiated and sustained between a work piece and an electrode. The electrode is then moved along the joint to be welded. The function of the electrode is to conduct a supplied current and to sustain the electric arc between the electrode's tip and the work piece. There are two types of electrodes: consumable and non-consumable. The consumable electrode is specially prepared so that it not only conducts current and sustains the arc, but it also melts and supplies filler metal to the weld site.
At present, welding in moisture or oil contaminated environments is accomplished by various means such as: preheating; isolation from the environment; electrode coating systems; shielded gas systems; flux core systems, and edges-to-be-joined coating systems. The electrode hard coating acts as a fluxing agent, which prevents, dissolves, or facilitates removal of oxides and other undesirable surface substances within limits. By creating a reducing or non-oxidizing atmosphere enveloping the arc, the electrode hard coating helps prevent contamination of the metal by oxygen, hydrogen, steam and nitrogen. Absent such a reducing atmosphere, the oxygen would readily combine with the metal causing porosity and oxidation of the weld. Reaction with nitrogen would cause brittleness, low ductility and possibly low strength and poor corrosion resistance. The electrode hard coating also facilitates arcing by insulating the sides of the electrode so that the arc is concentrated to a confined area. In addition, the electrode hard coating serves as a thermal insulator.
In other arc welding processes the shielding gas envelope of a non-oxidizing or reducing atmosphere is achieved by gas directed to the weld using an uncoated electrode (such as TIG, Tungsten Inert Gas; and MIG, Metal Inert Gas systems). Such an atmosphere can also be obtained with flux-cored welding rods. The flux produces a reducing or non-oxidizing atmosphere inside the electrode with a bare or lightly coated (copper flashing) surface. Alternatively, a submerged arc can be created with the electrode surrounded by granulated fluxing material. The fluxing material excludes air by forming liquid under which the arc is submerged.
The electrode hard coatings reduce impurities such as oxides, sulphur and phosphorous which tend to impair the deposited weld, and aid in ionization and maintenance of the arc. Electrode hard coatings provide material such as silicates, which forms a slag over the deposited weld. The slag retards heat transfer between the deposited weld and the surrounding environment and allows the deposited weld to cool and solidify slowly. The slow cooling eliminates entrapment of gases within the weld, permits solid impurities to float to the surface and has an annealing effect on the deposited weld.
There are four types of electrode hard coatings in general use. These are iron powder coatings, cellulose coatings, mineral coatings and combination of the cellulose and mineral coatings. Conventional electrode hard coatings contain some or all of cellulose, limestone fluorspar, rutile, titania, asbestos, iron powder, iron oxide, clay ferro-silicon, ferromanganese, and sodium silicate.
Specifications for electrode hard coatings are issued by the American Welding Society and American Society for Testing Materials. Suitable electrode hard coatings for use with the invention include American Welding Society AWS 3, AWS 4, AWS 6, AWS 8 designation electrode coatings. Other electrode hard coatings can be used with maintenance electrodes, non ferrous electrodes and others which do not conform to published specification.
Similar benefit in submerged arc and flux core arc welding is achieved when hard coating type material is provided as a granular surrounding material or internally in the electrode. In the case of submerged arc welding there are specifications for fluxes and wire. In case of flux cored arc welding the American Welding Society has no classification system. Fluxes generally are considered to be proprietary products.
When welding in air within contamination limits, the electrode's hard coating provides a slag deposit which coats and protects the deposited weld. However, the limits of moisture or oil contamination in field conditions are often exceeded causing inefficient welding and faulty welds. The resulting contaminant inclusion and undesirable rapid cooling of the deposited weld may cause embrittlement of the deposited weld. Thus, if adequate protection from said contaminants is not provided, the strength and ductility of welds formed in heavily moisture or oil contaminated areas, typically are lower than that obtainable in uncontaminated areas.
One object of the invention is to provide a contaminated environment welding electrode capable of producing welds of greater strength and ductility than previously possible. Another object of the present invention is to provide a contaminated environment electrode with improved heat distributing characteristics by minimizing thermal stressing and more efficiently retarding heat loss. Yet another object of the present invention is to provide a contaminated environment welding electrode with enhanced arcing capability which will allow longer and varying arc lengths equal or better than those encountered in ideal welding conditions. Still another object of the present invention is to provide a contaminated environment welding electrode which allows smoother, more efficient welding. Yet another object of the present invention is to provide a simple electrode to allow the conventional welding with less pretreatment in moisture and oil contaminated areas, enabling welders with less skill and training to function suitably. Another object of the present invention is to provide a dry powder or metallic coating on pieces to be welded which will volatilize approximate to the weld arc, imparting to the weld formed greater strength and ductility than previously possible. A further object of the present invention is to provide an electrode for welding in hyperbaric conditions.